Need to speedup the website drastically

I have a dedicated server and I have 1 main website to run at top speed. The other sites on the server (10) have only a few viewers a day so they are not taking any server power.

The one that I need to run at full speed is a WP site with 62 active plugins (tons from WPMU) - On of them is your image optimizer and I also have WP Rocket to cache the site.

I currently see around 9 seconds for a page to load (82% slower than average) and I have 0 traffic on this site (still building up content on it).

What can be done other than Cache and Image optimization? I am really far from my objective of having things showing up at a blink of the eye.

Thank you Team!